add a DataSources entrypoint

[Ladicek]

Similarly to the Logging or Security entrypoints, there should be a DataSources entrypoint that would provide easier access to datasource commands builders. In addition to that, a simplified variant of the datasource commands builders should be added -- these simplified builders would only accept a small subset of the possible options and would provide a way to create the "full" builder. The DataSources entrypoint would primarily create these simplified builders.